Ophthalmology · Neurotrophic Keratitis

Symptoms, Diagnosis, and the Mackie Staging System

At a Glance

Neurotrophic keratitis can worsen without much pain because damaged corneal nerves reduce sensation. Blurred vision, redness, cloudiness, and dryness may signal disease; corneal sensation testing and Mackie staging show severity and risk to vision.

One of the most challenging aspects of neurotrophic keratitis (NK) is that your symptoms may not match the severity of the damage. Because the nerves that signal pain are the same ones that are damaged, your eye may look significantly worse to a doctor than it feels to you ^[1]^[2].

Identifying the Symptoms

In many eye conditions, a tiny scratch feels like a piece of glass in the eye. In NK, you might have a large ulcer and feel almost nothing ^[3]. Because of this, you must rely on visual cues rather than physical feelings. Common signs include:

Blurred or fluctuating vision: This is often the first thing patients notice ^[4].
Redness: Your eye may appear chronically “bloodshot” ^[3].
Cloudiness: The clear window of your eye (the cornea) may look hazy or gray ^[3].
Dryness: You may feel like your eye is dry, but without the typical sharp “stinging” sensation ^[5].

Testing Your Sensation

To help diagnose NK, your doctor will test how much your cornea can “feel.” This is known as corneal sensation testing ^[4]. There are two common ways this is done:

The Cotton Wisp Test: This is a quick, qualitative test. The doctor gently touches the cornea with a fine wisp of sterile cotton to see if you blink or feel the touch ^[4]. While useful, it is often not sensitive enough to catch early nerve loss ^[6].
Cochet-Bonnet Esthesiometry: This is a more precise, quantitative test. The doctor uses a device with a thin, retractable nylon filament ^[7]. By adjusting the length of the filament, they can measure exactly how much pressure is needed for you to feel it. A common scale is 0 to 60 millimeters ^[8]. While some clinicians reference a measurement below 40 mm as an indicator, there is no single cutoff that diagnoses every patient; it depends on the instrument, age, and comparison to your other eye ^[6]. The measurement helps support the diagnosis and track changes over time.

The Mackie Staging System

Doctors use the Mackie Classification to categorize the severity of NK. This staging is vital because it determines your treatment plan ^[9].

Stage	Name	What is happening?
Stage 1	Epithelial Alterations	The top layer of the cornea (the epithelium) is intact but unstable. You may have punctate keratitis—tiny, pinhead-sized dry spots on the surface ^[1]^[3].
Stage 2	Persistent Epithelial Defect (PED)	The top layer of cells has broken down, creating a “sore” or “hole” that does not heal on its own. This area often has smooth, rolled edges ^[1]^[10].
Stage 3	Corneal Ulceration	The damage has moved deeper into the stroma (the middle layer of the cornea). This can lead to serious thinning, “melting,” or even a perforation of the eye ^[1]^[9].

Why Staging Matters for Your Vision

The stage at which you are diagnosed acts as a “weather report” for your recovery. While treatment can be effective at any stage, the best chance to reverse damage and protect your vision is during Stage 1 ^[11]^[9].

By the time the disease reaches Stage 3, there is a higher risk of permanent scarring (fibrosis), which can permanently cloud your vision even after the surface has healed ^[12]^[13]. This is why your medical team will monitor you closely to ensure a Stage 1 or 2 condition does not progress deeper into the eye tissue ^[13].

Common questions in this guide

What symptoms can neurotrophic keratitis cause if the eye does not hurt?

Neurotrophic keratitis can cause blurred or fluctuating vision, redness, cloudiness, and dryness with little or no pain. Reduced corneal sensation means that serious surface damage may not feel as severe as it looks. A lack of pain does not mean the condition is mild.

How do doctors diagnose neurotrophic keratitis?

Doctors check the surface of the cornea and measure how well it senses touch. They may use a cotton wisp for a quick check or a Cochet-Bonnet esthesiometer for a more precise measurement. The result supports the diagnosis and helps track changes over time, but no single number applies to every patient.

What do the three Mackie stages of neurotrophic keratitis mean?

Stage 1 means the corneal surface is still intact but unstable and may have tiny dry spots. Stage 2 means there is a persistent epithelial defect, or an open area that does not heal normally. Stage 3 means the ulcer has reached the deeper corneal layer and may cause thinning, melting, or a hole in the eye.

What does a low corneal sensation test result mean?

A lower measurement on a Cochet-Bonnet test generally indicates reduced corneal sensation. Doctors interpret the number in context, including the instrument used, your age, the other eye, and different areas of the cornea. There is no universal cutoff that diagnoses every patient.

Can neurotrophic keratitis permanently affect vision?

It can, especially if the condition progresses to deeper ulceration. Stage 3 disease has a greater risk of thinning, perforation, and scarring that may permanently cloud the cornea even after the surface heals. Finding and treating the disease earlier gives the best chance of protecting vision.

What changes should I watch for between eye appointments?

Pay attention to new or worsening blurred vision, redness, cloudiness, or dryness, even if there is little pain. Notice whether eye drops feel different on the surface or whether you are blinking less often. Report concerning changes promptly because neurotrophic keratitis can worsen without strong warning symptoms.

Curated prompts to bring to your next appointment.

1.What is my current Mackie stage, and is there any evidence of stromal involvement (Stage 3)?
2.What was the exact measurement of my corneal sensation in millimeters when using the esthesiometer?
3.How do my sensation levels compare between my two eyes and across different areas of my cornea?
4.Is the surface of my eye currently showing 'punctate keratitis' or a 'persistent epithelial defect'?
5.Given my stage, what is the risk of my cornea thinning or 'melting' if we don't change the current treatment?

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References (13)

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3
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11
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This page is for informational purposes only and does not constitute medical advice. An ophthalmologist should interpret your corneal findings and Mackie stage and advise you about care for your eye.

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